Oscillator for sine waves and square waves



April 11, 1944. J. F. RIDER 2,346,396

OSCILLATOR FOR SINE WAVES AND SQUARE WAVES Filed Jun e. 50,1942 I 29 mamflnventor @MZ'I'IZzder i i mm attorney Patented Apr. 11, 1944 OSUILEATOR' F'OR SINE WAVES AND? SQUARE WAVES John Rider, New York; N. Y... assignor toRadio Corporation ofAmerica, a corporation of'Delaware Application. June- 3.0, 1942,. Serial No.. 449 069 (Cl. 2530--36i 4' Claims;

\ invention relates to oscillators of the. resistor capaoitor type. having: not resonant. cir.--

cuits and particularly to oscillators designed" to j supply signals covering a. wide range of predetermined. frequencies: for. measuring or testingpurposes or the like.

For measuring and: testing equipment, it is sometimes desirable;- to have available either a sine wave signal or: a square wave signal which may be.- produced at known frequencies within: awid'eirequency range. The usual practice has. been to obtain. such signals. from. separate. sine wave: and square wave. generators.

object of the present invention; is to. pro-' vide an improved. simple and.v reliable oscillator circuit for producing at predetermined frequen-- cies either a sine'wave outputor; a. square wave' output.

In a preferred embodiment of the invention, the oscillator-comprises two vacuum tubes which are: resistance coupled and which. are. provided withboth regenerative and degenerative ieed' back circuits. The; regenerative circuit includes a. resistor capacitor network; that has a. fre quencyselectivity characteristic wherebysinei wave. oscillators may be produced; the harmonic frequency components: being held: to very small amplitudes by the: small ratio of regeneration to, degeneration at the harmonic frequencies.

12' have. discovered that by changing someof. the circuit. elements to: decrease the amountot degeneration, the oscillator changes to: a square wave oscillator whereby it is possible, by means of a simple. switching arrangement, to obtain from the circuit either sine waves: or' square waves.

The invention will bebetter understood from: the following description. taken in connection the accompanying drawing in which Figure 1' is a circuit: diagram of an: oscillator embodying my invention, and

Figures 2a. and 2b. are graphs: which are re-* ferred to; explaining the. operation of: the

circuit of Figure 1' as a square wave oscilclaa tor.

Figure: 1 illustrates: a particular" embodiment of the invention comprising a pentode In and a pcntode 3. The anode orplate" H1" of pentode fll is resistance coupled to the control grid" i2; of a pentode [3, by means of a coupling condenser M, the plate resistor 16 of pentode t and the: grid leak. resistor ll of pentode [3. Positive D. C. voltages from a suitable source (not shown) are supplied to the anode H of tube Ill and to the anode l8 of tube [3 through resistors I26 and I9, respectively-z Suitable positive volts ages for thescreen; grids of tubes. In.- andg [3: are supplied from voltage divided; resistors it. 2-2 and 23; 24, respectively: A bypass capacitor, 25 is connected across resistor 22. A filter and voltage reducing resistor 26 and a filter capacitor 21 may be provided in the-anodeandscreen grid voltage supply circuit-- for the pentode; l9. A suitable operating: bias for the; tube. l3: may be provided by a: cathode resistor 15- which is by-- passed. by a capacitor 20-.

Regenerative feedback is provided from the anode of tube I3 througha coupling or} blockingcapacitor 28-, one of the resistors 29a; 29b, 29c or 29d, and the variablecapacitors 31a and 31b in series therewith to the control grid 30 of the, tube Ill. The regenerative circuit also includes a parallel resistor-capacitor combina. tion. in they control grid circuitof' the tube In. This. parallel combination comprises, variable capacitors 320 3212 and. 320 connectedubetween the grid 30 and ground and shunt relation to one of the resistors 33a, 33b; 330 or 33d which are: likewise connected betweenthe grid 30 and ground. By switching: in: difierent resistors and/or by changing the; capacity of. capacitors in the regenerative. feedback circuit, the; frequency of the oscillator output may be changed to; diiferent values indicated by calibrated dials or the like (not shown).

Degenerative feedback is also provided by coupling the1 anode of tube Hi. tothe cathode of tube l llthrough the capacitor-28,aconductor: 36 and resistors 31. and 38, andj by includingresi'stance, between the; cathode of tube: l0 and ground preferably in-theform. oftungsten filament lamps, H and 4-2. The lamps may be shunted byf-a capacitor 35. The:- lamps. H and 42 in the. example illustrated areillO- volt, 6 watt, tungsten filament, lamps. They may be replaced by other elements having a positive temperature ooefiicient- Or by resistors which do; not change in resistance value during: operation of the oscillaton Positive temperature coeflicient devices are preferred, however, becausethey control the amplitude of oscillation oi the. oscillator due to the fact that theamount of. degeneration is increased when the. resistance of such dc.- vices is increased in response to an; increase in amplitude of oscillation. I

Switches 43 and 44 are. provided across the lamp; 42 and the resistor 31. respectivelyy for switching the oscillator to either sine wave or square wave oscillation. These switches may be ganged as indicated by the broken line. With sufiicient to reduce to a small amplitude anycomponents differing in frequency from that at which maximum regeneration occurs.

The oscillator operates as a square wave os-..

cillator, however, when the switch 43 is closed and the switch 44 is opened so thatthe amount of degeneration is greatly reduced. The frequency of oscillation simultaneously goes to oneput and input circuits of the second and first tubes, respectively, to hold to a comparatively small amplitude any signal components other than the signal component at said predetermined frequency whereby a sine wave output is produced and switching means for reducing said degenerative coupling sufficiently to cause the oscillator to change its modeof oscillation and oscillate to produce a square wave output.

,3. An oscillator for producing either a. sine wave output or a square wave output which includes two amplifier tubes each having an input circuit and an output circuit, means for coupling the output circuit of the first of said tubes half of the frequency of oscillation as a sine wave oscillator.

wish to limit the invention to any particular theory of operation. When operating'in this manner, the voltage between the anode I l of the tube [0 and ground has the wave shape shown in'Fig. 2a., while thevoltage at the output, 1. e, between the anode N3 of tube l3 and ground,

has the wave shape shown in Fig. 2b.

In the drawing, the tube types and the values of various circuit elements have been indicated, merely by way of example in microfarads, micromicrofarads, megohms and thousands of ohms, the latter being indicated by the letter k.

I claim as my invention: I 1; An' oscillator for producing either a sine wave output or a square wave output which in cludes two amplifier tubes each having an input circuit and an output'circuit, means for coupling the output circuit ofthe first of said tubes to the input circuit of the second of said tubes,- resistor-capacitor means for regeneratively coupling the output circuit of said second tube to the input circuit of said first tube, said regenerative coupling circuit having a frequency response such that it provides more regeneration at a predetermined frequency than at any other frequency, meansfor providing suificient degenerative coupling between the output and input circuits of the second and first tubes, respectively, to hold to a comparatively smallamplitude any signal components other than the signal component at said predetermined frequency wherebyf a sine wave output is produced and switching means for reducing said degenerative coupling sufiiciently to cause the oscillator to change its mode of oscillation and oscillate to produce a square wave output.

' 2. An' oscillator for producing either a sine "wave output or a square wave output which includes two amplifier tubes each having an input circuit and an output circuit, means for con-,-

the input circuit of said first tube, said regenerative coupling circuit having a frequency response such that it provides more regeneration at a predetermined frequency than at any other frequency, means including a resistor element in the common part of the anode-cathode, grid- .cathode circuits of said first tube for providing sufiicient degenerative coupling between the out- It appears likely that the apparatus now operates as a multivibrator but I do not to the input circuit of the second of said tubes,

resistor-capacitor means for regeneratively coupling the output circuit of said second tube to the-input circuit of said first tube, said regenerative .coupling circuit having a frequency respouse such that it provides more regeneration at a predetermined frequency than at any other frequency, means for providing sufilcient degenerative coupling between the output and input circuits of the second and first tubes, respectively, to hold to a comparatively-"small amplitude any signal components other than the signal component at said predetermined frequency whereby! a sine wave output is produced, said degenerative coupling means including two serially connected resistor elements in the common part of the anode-cathode, gride-cathode circuits of said first tube which have a positive temperature coefilcient, and switching means for shorting out one of said resistor elements and thereby reducing said degenerative coupling sui-' ficiently to cause the oscillator to change its mode of oscillation and oscillate to produce a square wave output. 1

4. An oscillator for producing either a sine wave output or a square wave output which includes two amplifier tubes each having an input circuit and an output circuit, means for coupling the output circuit of the first of said tubes to the input circuit of the second of said tubes, resistor-capacitor means for regeneratively cou-- pling the output circuit of said second tube to the input circuit of said first tube, said regenerative'coupling'circuit having a frequency re-. sponse such that it provides more regeneration at a predetermined frequency than at-any other frequency, means including resistance in the common part of the anode-cathode, grid-cathode circuits of said first tube for providing sufficient degenerative coupling between the output and input circuits of the second and first tubes. respectively, to hold to a comparativelysmall amplitude any signal components other-than the signal component at said predetermined frequency whereby a sine wave output is produced, said degenerative coupling means also including a resistive connection from the plate ofthe sec-. ond tube to the cathodeof the first tube, and switching means for reducing said degenerative coupling suiiicientlyi to cause the oscillator- 1:0 change its mode of oscillation and 0SCi11&te."t0 produce a square wave output, said; switching means including means for shorting out part of said resistance located in the common part of said anode-cathode, grid-cathode circuits and for increasing the resistance of' said resistiv connection.

JOHN F. R IDERQ 1 

